This invention relates to a maneuvering system of watercraft and the like provided with maneuvering equipment comprising a plurality of maneuvering devices, such as thrusters and main screws.
Offshore rigs of a semi-submergible type or a floating type or some type of workboat, such as tug boats, supply boats etc., are required to turn around with a small radius of turning movement or on the spot in view of the nature of operations to be performed by them. These watercraft are generally low in speed and have quite a difficult steerage when an ordinary rudder is used. To accomplish the object, proposals have been made to use a special maneuvering system for this type of watercraft. For example, in the case of offshore rigs of the semi-submergible type which are square in shape, four steerable thrusters are used each of which is mounted on a column at one of four corners of the rig. In the case of workboat, a plurality of rotatable jet thrusters and propulsion units capable of varying the direction of thrust are mounted in the bow and stern to constitute maneuvering equipment. Thrusts generated by these maneuvering devices are combined to obtain a desired propulsion or turning movement.
In ordinary merchantmen, there are examples of a bow thruster and a stern thruster being used for maneuvering a ship in bringing her into a position alongside a wharf in a port or out of such position, so that the ship can be made to move in a desired movement by these maneuvering devices in cooperation with an ordinary maneuvering device, such as a main screw.
In a maneuvering system of watercraft and the like of the aforesaid construction comprising a plurality of maneuvering devices constituting maneuvering equipment, it has been usual practice to provide each of the maneuvering devices with operating means to maneuver the vessel by individually operating the maneuvering devices through the associated operating means. In maneuvering the vessel by the aforesaid process, the problem has been raised that the operation is complicated and the response of the maneuvering devices is slow, because various maneuvering devices should be actuated in such a manner that a maneuvering device suitable to meet a specific vessel steering requirement is operated at an opportune time by an operator well versed in the action of the particular maneuvering device on the ship's hull.
In a vessel provided with a plurality of maneuvering devices, the maneuvering devices each impart to the hull a thrust individually produced by the maneuvering device. What is required in maneuvering a vessel is a resultant thrust in the form of a sum of vectors of the geneated thrusts and a sum of turning moments produced by the generated thrusts. If, for example, a joy-stock control system consisting of one joy-stick lever and dial knob can be used for controlling the resultant thrust and the sum of the turning moments, it would be possible to maneuver the vessel as desired irrespective of the number and type of the thrusters used, thereby enabling the aforesaid problem of the prior art to be obviated and allowing maneuvering to be achieved in a manner to meet the steering requirements.
A maneuvering system capable of controlling the resultant thrust and the sum of the turning moments offers the aforesaid advantage. However, such maneuvering system is not without disadvantages. One of them is that when some of the maneuvering devices are unable to generate thrusts commensurate with an instruction on account of such maneuvering devices being shut down or the value of instruction being higher than the capacities of the maneuvering devices, the resultant thrust and the sum of the turning moments would be influenced in a complicated manner, thereby making it impossible to continue maneuvering of the vessel.